Space disinfection

ABSTRACT

A method for disinfecting a volume or surfaces bounding a volume comprising nebulising a solution comprising a sterilizing agent in a solvent having a lower boiling point than the sterilizing agent, for example ultrasonic nebulization of aqueous hydrogen peroxide, to form a nebulant. The nebulant is subjected to energy of a kind and for a duration sufficient to vaporize solvent in preference to sterilizing agent, eg heating element means, infra red, laser, microwave, RF or other radiation generating means; induction heating means; heat exchanger means; conduction means; convection means; or mechanical energy transfer means to increase the concentration of the agent in the nebulant particles. Vaporized solvent is removed from the gas stream at or above atmospheric pressure and, if necessary, the nebulant is cooled to below 70° C. The volume or surfaces are exposed to the nebulant for a time sufficient to sterilize said volume or surfaces. Also, apparatus for carrying out the method.

REFERENCE TO CORRESPONDING APPLICATIONS

The present application is a continuation of U.S. application Ser. No.11/997,878 which is a U.S. National Stage Application of InternationalApplication No. PCT PCT/AU2006/001115, filed Aug. 4, 2006, and is nowU.S. Pat. No. 8,444,919, and claims priority to Australian PatentApplication No. 2006900748, filed Feb. 15, 2006, and Australian PatentApplication Nos. 2005904181, 2005904196, and 2005904198 all filed onAug. 4, 2005.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for disinfectingor decontaminating large exposed surfaces or spaces which may beinfected with bacteria, fungi, viruses, or fungal or bacterial spores.

A space to be disinfected may be a chamber, for example, a shippingcontainer, a hospital operating theatre or hospital ward, an aircraftinterior, or may be a shopping mall, subway system, warehouse, silo, orother enclosed or semi-enclosed space. Exposed surfaces may beexemplified by surfaces of walls or partitions defining the space, orwork surfaces, machinery surfaces, air conditioning ducts, or othersurfaces which are interior or can be enclosed or partly enclosed, atleast temporarily, for the present purpose.

BACKGROUND OF THE INVENTION

Any discussion of the prior art throughout the specification should inno way be considered as an admission that such prior art is widely knownor forms part of common general knowledge in the field.

The most commonly used method for disinfecting such large spaces andsurfaces involves the use of gases such as ozone or chlorine dioxidewhich are oxidative or corrosive and toxic, or may involve gases such asethylene oxide or aldehydes, such as glutaraldehyde or formaldehyde,which are extremely toxic and which leave potentially harmful residueson surfaces. Steam is sometimes used and is hazardous to the operatorbecause of the high temperatures involved and leaves a dense moisture onthe surface which may lead to rusting.

From a health and environmental perspective it would be preferable touse hydrogen peroxide or peracetic acid as a disinfectant. Hitherto, asdiscussed in Ronlan U.S. Pat. No. 6,500,465, high density fine aerosols(aerosol droplet diameter less than 50 microns) of peracetic acid orhydrogen peroxide suitable for disinfecting have only been consideredstable at 100% relative humidity.

Also hitherto, aerosols have suffered from the general problems thatthey were not effective at penetrating covered surfaces. This meant thatdoor locks, hinges and the like as well as occluded surfaces such as,for example, an area of floor beneath a chair, could harbour organisms.

Another problem is that aerosol particles tend to settle and wet out thesurfaces on which they fall, leaving an undesirable residue on thesurface which must be cleaned off. In our co-pending Australian PatentApplications 2005904196, filed Aug. 4, 2005, entitled, “ImprovedAerosol” and 2006900748, filed Feb. 15, 2006, entitled, “MembraneSterilization” the content of which is incorporated by reference,sterilising or disinfecting agents are disclosed which can be adaptedfor treating large surfaces or spaces.

OBJECT OF THE INVENTION

Its an object of this invention to provide a method for disinfecting alarge area or disinfecting a volume and which avoids or ameliorates atleast some of the disadvantages of the prior art. It is a further objectof the invention to provide improved apparatus and improved fumigantsfor carrying out the method.

By disinfecting a volume is meant that the air in the volume andorganisms if any suspended in the air are disinfected.

It is an object of preferred embodiments to be able to disinfectsurfaces in chambers such as operating theatres, wards of hospitals,cold rooms, refrigerators, vans, sea containers, factory areas wheredisinfection is a requirement and preferably to do so by means which arescalable.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words ‘comprise’, ‘comprising’, and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to”.

BRIEF STATEMENT OF INVENTION

According to a first aspect the present invention provides a method fordisinfecting an area or a volume comprising the steps of:

(1) nebulising a solution comprising a sterilizing agent in a solvent toform a nebulant of finely divided particles of the solution in a gasstream, said solution including a solvent having a lower boiling pointthan the sterilizing agent;

(2) subjecting the nebulant to energy of a kind and for a durationsufficient to vaporize solvent in preference to sterilizing agent,whereby to increase the concentration of the agent in the nebulantparticles;

(3) removing solvent vaporized in step 2 from the gas stream at or aboveatmospheric pressure and, if necessary, cooling the nebulant to below70° C.; and

(4) exposing said surface to nebulant from step 3 for a time sufficientto disinfect said area or volume.

In preferred embodiments the nebulant is a solution of hydrogen peroxidein water, desirably at an initial concentration of 35% or less. Ifdesired the method can sterilize said surface, or the surfacescontaining said volume

According to a second aspect the invention provides a method fordisinfecting a large area or volume comprising the steps of :

(1) exposing said surface to, or introducing to said volume, a nebulantcomprising a solution of hydrogen peroxide in water; and

(2) controlling the relative humidity in the volume or in the vicinityof said surface to from 20% to 70% RH.

The invention will now be more particularly described by way of exampleonly with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic of a space disinfection apparatus in accordancewith an embodiment of the invention.

FIG. 2 shows a schematic for a nebuliser for use in accordance withembodiments of the invention.

FIG. 3 shows a schematic for a nebuliser for use in accordance withembodiments of the invention.

FIG. 4. shows a schematic of a membrane concentrator for use inaccordance with embodiments of the invention.

DETAILED DESCRIPTION

With reference to FIG. 1 there is shown schematically a first embodimentof the invention. In FIG. 1 there is shown in vertical cross-section achamber 1 to be disinfected. Chamber 1 is defined is by walls 2, 3,floor 4, and ceiling 5 (the remaining walls and entry not beingillustrated. Within the chamber is an ultrasonic nebuliser 6 for exampleof the kind described in our copending application “Improved Aerosol” atFIGS. 3 and 4, which are shown here as FIGS. 2 and 3. Nebuliser 6 is fedin this example with a 35% solution of hydrogen peroxide in watercontained in a reservoir 7 via feed line 8. Nebuliser 6 draws air at airinlet 9, in this example from within Chamber 1. The nebulant generatedby nebuliser 6 exits at nebulant outlet 10 and is drawn via a conduit 11on the suction side of fan 12 and pumped from the pressure side of fan12 to a heater 13. Nebulant from nebuliser 6 passes over a heaterelement in heater 13 and is directed from heater outlet 14 via conduit15 to a disperser 16 from where it permeates the chamber volume.Moisture removal unit 20 draws air from within chamber 1 at 21, coolsand dehumidifies it and returns it to the room at a predeterminedtemperature and relative humidity. In the present example moistureremoval unit 20 is an air conditioning system.

In operation nebuliser 6 nebulises a solution comprising hydrogenperoxide in water from reservoir 7 to form a nebulant of finely dividedparticles of the solution in the air stream. The water has a lowerboiling point than the hydrogen peroxide In this example the nebulant isheated in heater 13 sufficiently to vaporize water in preference toperoxide, whereby to increase the concentration of the peroxide in thenebulant particles to around 60-70% and reducing the particle size asdiscussed in our co-pending applications.

Disperser 16 may be one or more baffles, which may be stationary ordriven or may be other means such as a fan for dispersing the nebulant.In this embodiment of the invention the water vapour removed from thenebulant during passage through heater 13 is removed from chamber 1 byair-conditioning system 20 at or above atmospheric pressure which drawsnebulant and water vapour from the room removes water vapour and returnscooled nebulant into the space.

The treated nebulant consists of particles having a smaller size (nanoparticles) than untreated particles produced by the nebuliser (microparticles) and therefore having a much lesser tenancy to settle out ofthe gas stream. The smaller particles also have a much greater rate ofdiffusion and ability to penetrate into covered spaces. The treatednebulant has a much higher concentration than the untreated nebulant orfeed solution. In our co pending application “Improved Aerosol”,nebulant from the nebuliser was heated in a heat exchanger and thencooled in a condenser to remove water (with reference to FIG. 2 of thatapplication, vapour from nebuliser 5 is heated in 17 and then cooled in20 to remove water). In the present FIG. 1, by controlling the relativehumidity within space 1 by air conditioner 20 a similar effect isobtained as was obtained in the examples of our co pendingspecification.

As described in more detail in our co pending applications:

-   -   Other sterilizing agents may be used and the sterilizing agent        may be dissolved in other solvents,    -   Other kinds of nebuliser may be used    -   Other gases may be fed to the nebuliser    -   Solutions of hydrogen peroxide solution in air are highly        preferred.    -   The solvent may be removed in preference to the biocide by        supplying energy in other ways    -   Water may be removed from the chamber by other means    -   It is desirable to control the relative humidity, and        temperature within predetermined limits as therein detailed.

In the present application the air conditioning may take the form of aducted room system or may be a portable unit placed in the room. Theunit need not employ a condenser but may be for example a desiccatorsystem such as a twin cycle system which absorbs moisture during onecycle, and is then dried venting the moisture externally during a secondcycle while a twin unit absorbs moisture, or a device such as disclosedin our copending “Membrane Concentrator” application, for example, adevice shown in FIG. 4 in which a current of nebulant enters conduit 171at 173 and exits at 174 and countercurrent of air or another dry gas 176pass on either side of a semipermeable membrane 172. The nebulantdroplets exiting at 174 are more concentrated than when they enter at173.

A catalytic destructor may be employed to remove excess peroxide fromthe chamber. The reservoir, nebuliser, fan, and heater may be combinedin a portable unit which can be moved from chamber to chamber, and ifdesired a separate air drying or air conditioning system may be madeportable for use in the same chamber as the nebuliser or may be combinedwith the nebuliser unit.

A preferred embodiment will now be described by way of example In thisembodiment 35% hydrogen peroxide in water was used as the biocide. Thecomponents of the device included a nebuliser array, (6×2 cm diametertransducers in a circular array), a heater element, a first and secondfan and a dehumidifier system. The dehumidifier used had been a smallair conditioning unit positioned appropriately within the space. Thepurpose of the first fan was to propel nanoparticles from the heaterinto the space and the purpose of the second fan was to ensure an equaldistribution of the aerosol to all surfaces within the space.

It was found to be highly desirable that the transducers aresynchronized within the array otherwise the waveforms produced willpotentially cancel each other out within the liquid resulting in aninefficient production of peroxide nebulant to the heater.

EXAMPLE 1

Tests were conducted in an 8 cubic meter volume of cubic shape.

Samples were coated with an inoculum at levels of approximately log 6and air dried for 2 hours on the plastic petri dish (Techno-Plas,Australia) in a laminar flow cabinet. The samples were placed in variouspositions in the room including on the walls, floor and ceiling. In theexample below the samples were placed in the centre of the wall adjacentto the corner and on the floor approximately in the centre of the roomand were exposed to hydrogen peroxide nebulant treated as described withreference to FIG. 1.

Unless otherwise stated, the operating conditions were:

-   Solution: 35% peroxide-   Temp: 25 degrees-   RH: fluctuated 45% to ˜65%. Sometimes 75%-   Nebulizer array 2.4 MHz-   Peroxide vapour: 300-500 ppm-   Air flow post heater: 400-600 cubic meters per hour.-   Heater Temp: 80-90 degrees-   Peroxide delivery: Optimally approximately 0.75 gram per cubic meter    per-    minute, ie 12.6 grams for the 8 cubic meter room.

The results obtained for various bacteria was as follows:

(In the tables “TNTC”=too numerous to count, “ND”=not done)

Table 1 shows the results for an experiment in which open carriers wereused.

Table 2 shows the result for the same conditions except that thecarriers were in closed petri dishes, i.e. dishes with lids. ClosedPetri dishes allow penetration across very narrow gaps. The dishes andlids are specifically designed to allow gas exchange with an incubatorenvironment while keeping the dish free from external microbialcontamination.

Table 3 and Table 4 show the results for Aspergillus niger.

EXAMPLE 2

The test of example 1 was repeated in a 69 cu m. chamber undersubstantially the same conditions except as shown in table 5

Table 5 shows the scalability of the process to a 69 cubic meter room.

In general, results with Bacillus stearothermophillus showed thatgreater than 6 log reductions could be obtained at 550 ppm on both thewalls and floor.

EXAMPLE 3

Air was recirculated through a catalytic destructor system (employing inthis example a mixture of metal oxides including aluminium oxide) to“decontaminate” the room by removal of excess peroxide. Otherwise theperoxide can be more slowly broken down by recirculating the conditioneddry air within the space or possibly by increasing the temperature tohelp facilitate the process. It took approximately one hour to reducethe peroxide vapour levels to about 10 ppm from a maximum ofapproximately 400-700 ppm in a 16 cubic meter room. The final 10 ppmtook much longer to reduce to a significant degree.

To an extent which is obvious from the disclosure herein contained,features disclosed in this specification may be combined with featuresor combinations of features disclosed in our co pending applications andsuch combinations are within the scope of the invention hereindisclosed.

TABLE 1 Peroxide Location vapour Contact Floor Wall Room level time (log(log Species size (ppm) (min) reduction) reduction) Pseudomonas 8 cubicaeruginosa meters (open carriers) 50 2.5 TNTC 3.5 5 TNTC 3.6 10 TNTC 4.320 ND ND 200 2.5 4.4 5.7 5 5.2 5.7 10 3.4 5.7 20 5.7 5.7 350 2.5 6.1 4.45 6.1 5.8 10 6.1 6.1 20 6.1 6.1

TABLE 2 Peroxide Location vapour Contact Floor Wall Room level time (log(log Species size (ppm) (min) reduction) reduction) Pseudomonas 8 cubicaeruginosa meters (closed carriers) 300 5 ND 6.7 10 ND 6.3 20 5.8 6.7

TABLE 3 Peroxide Location vapour Contact Wall Wall Room level time (log(log Species size (ppm) (min) reduction) reduction) Aspergillus 8 cubicOpen Closed niger meters carriers carriers 250 5 6.3 5.1 10 6.3 6.3 206.3 6.3 30 6.3 6.3 500 5 6.9 6.9 10 6.9 6.9 20 6.9 6.9 30 6.9 6.9

TABLE 4 Location Peroxide Floor Wall vapour Contact (log reduction) (logreduction) Room level time Open Closed Open Closed Species size (ppm)(min) carriers carriers carriers carriers Aspergillus niger 8 cubic 35015 6.5 6.1 5.9 5.7 meters 550 15 6.7 6.6 6.7 6.3 20 7.5 7.5 7.5 7.5 307.5 7.5 7.5 6.6

TABLE 5 Peroxide Location vapour Contact Floor Wall Room level time (log(log Species size (ppm) (min) reduction) reduction) Aspergillus 69 cubic500 niger meters closed 30 6.7 6.7 open 30 6.7 6.7

1-15. (canceled)
 16. An apparatus for disinfecting a volume or surfacesbounding a volume comprising: a nebulizer to produce a nebulantcomprising finely divided particles of a solution suspended in a gas,the solution comprising a sterilizing agent a solvent; means forsupplying sufficient energy to the nebulant to selectively vaporize atleast some of the solvent to increase the concentration of thesterilizing agent in nebulant particles; and a disperser comprising oneor more baffles or a fan for contacting the volume or surface to bedisinfected with the nebulant.
 17. The apparatus according to claim 16wherein the means for supplying sufficient energy to the nebulant toselectively vaporize at least some of the solvent comprises heatingelement means, infra red, laser, microwave, RF or other radiationgenerating means; induction heating means; heat exchanger means;conduction means; convection means; or mechanical energy transfer means.18. The apparatus according to claim 16 wherein the means for supplyingsufficient energy to the nebulant to selectively vaporize at least someof the solvent comprises a heating element.
 19. The apparatus accordingto claim 16 further comprising means for separating solvent vapor fromthe gas at atmospheric pressure.
 20. The apparatus according to claim 19wherein the means for separating solvent vapor from the gas comprises adrying agent, a molecular sieve, a membrane, a centrifuge, or a cyclonicseparator.
 21. The apparatus according to claim 19 wherein the means forseparating solvent vapor from the gas at atmospheric pressure ispositioned downstream of the disperser.
 22. The apparatus according toclaim 16 wherein the nebulizer comprises a device selected from thegroup consisting of ultrasonic nebulizers, sprays, jet nebulizers andpiezoelectric nebulizers, operated continuously or cyclically.
 23. Theapparatus according to claim 16 wherein the disperser comprises a fanfor contacting the surface to be disinfected with the nebulant.
 24. Theapparatus according to claim 16 further comprising a fan or pump betweenthe nebulizer and the means for supplying sufficient energy to thenebulant to selectively vaporize at least some of the solvent.
 25. Theapparatus according to claim 16 further comprising a catalyticdestructor for removing sterilizing agent from the volume or surface.26. A portable apparatus for disinfecting a volume or surfaces boundinga volume comprising: a nebulizer to produce a nebulant comprising finelydivided particles of the sterilizing agent solution suspended in a gas,the solution comprising a sterilizing agent a solvent; a sterilizingagent feed conduit in fluid communication with the nebulizer; a heatingelement configured supplying sufficient energy to the nebulant toselectively vaporize at least some of the solvent to increase theconcentration of the sterilizing agent in nebulant particles; a fan or apump positioned downstream of the nebulizer and upstream of the heatingelement to pass the nebulant over the heating element; and a dispersercomprising one or more baffles or a fan positioned downstream of theheating element for contacting the volume or surface to be disinfectedwith the nebulant.
 27. The apparatus according to claim 26 furthercomprising means for separating solvent vapor from the gas atatmospheric pressure.
 28. The apparatus according to claim 27 whereinthe means for separating solvent vapor from the gas comprises a dryingagent, a molecular sieve, a membrane, a centrifuge, or a cyclonicseparator.
 29. The apparatus according to claim 27 wherein the means forseparating solvent vapor from the gas comprises an air conditioningsystem.
 30. The apparatus according to claim 26 wherein the means forseparating solvent vapor from the gas at atmospheric pressure ispositioned downstream of the disperser.
 31. The apparatus according toclaim 26 further comprising a catalytic destructor for removesterilizing agent from the volume or surface.
 32. The apparatusaccording to claim 26 wherein the disperser comprises a fan forcontacting the volume or surface to be disinfected with the nebulant.33. The apparatus according to claim 26 further comprising a sterilizingagent solution reservoir in fluid communication with the sterilizingagent feed conduit.
 34. The apparatus according to claim 26 wherein thenebulizer comprises a device selected from the group consisting ofultrasonic nebulizers, sprays, jet nebulizers and piezoelectricnebulizers, operated continuously or cyclically.
 35. The apparatusaccording to claim 26 wherein the nebulizer comprises an ultrasonicnebulizer.